Hydrogen storage alloy is a functional material with high hydrogen-storage density. At present, hydrogen storage alloy could be roughly divided into six categories: rare earth based AB5 type, such as LaNi5; magnesium based, such as Mg2Ni, MgNi, La2Mg17; rare earth-magnesium-nickel based AB3-4 type, such as La2MgNi9, La5Mg2Ni23, La3MgNi14; titanium based AB type, such as TiNi, TiFe; zirconium or titanium based AB2 type with Laves phase, such as ZrNi2; vanadium based solid solution type as (V0.9Ti0.1)1-xFex.
The hydrogen-storage material widely used nowadays is LaNi5 type hydrogen-storage alloy. The alloy is mainly used as a negative material of a metal hydride-nickel(MH-Ni) secondary battery, with a theoretical electrochemical capacity of about 373 mAh·g−1. The commercial negative material electrode materials in actual application is Mm(NiCoMnAl)5 (wherein Mm denotes mixed rare earths), which has a maximum capacity of 350 mAh·g−1. In order to develop hydrogen-storage alloys with better electrochemical properties or higher hydrogen storage capacity, the research of magnesium based alloy has become a hotspot. Magnesium based alloys have high theoretical capacity. Especially, great progresses have been made in the study of rare earth-magnesium-nickel based AB3 type, A2B7 type and A5B19 type alloys and these alloys has been put into industrial application. Titanium, zirconium and vanadium based hydrogen storage materials were not widely used due to their disadvantages such as poor activation characteristic, high cost, etc.
CN201310228766.0 discloses an A2B7 type hydrogen storage alloy for nickel-hydride battery and preparation method thereof. The composition of the alloy conforms to the general formula LnaMgbNixYyZz, wherein Ln denotes one or more rare earth element(s), Y denotes one or more element(s) selected from Al, Co, Nb, V, Fe, Cu, Zn, As, Ga, Mo, Sn, In, W, Si and P, and Z denotes one or more element(s) selected from Ag, Sr, Ge, 0.5≤a<2, 0<b<1, 5<X+Y+Z<9, 0<Y<3, 0<Z<1.
CN101210294A discloses a A5B19 type alloy. The alloy has a formula of X5-aYaZb, wherein X denotes one or more of rear earth metals, Y denotes one or more of alkaline earth metal(s), Z denotes one or more element(s) selected from Mn, Al, V, Fe, Si, Sn, Ni, Co, Cr, Cu, Mo, Zn and B, 0<a≤2, 17.5≤b≤22.5.
CN102195041A discloses a hydrogen storage alloy for an alkaline storage battery. The alloy has a formula of LaxReyMg1-x-yNin-m-vAlmTv, wherein Re denotes at least one rare earth element(s) including Y(ytterbium)(except La), T denotes at least one element(s) selected from Co, Mn and Zn; 0.17≤x≤0.64, 3.5≤n≤3.8, 0.06≤m≤0.22, v≥0. The main phase of the alloy is A5B19 type crystal structure.
CN101238231A discloses a hydrogen storage alloy. The alloy contains a phase of Pr5Co19 type crystal structure, which conforms to the general formula A(4−w)B(1+w)C19, wherein A denotes one or more element(s) selected from rare earth elements including Y (yttrium); B denotes Mg element; C denotes one or more element(s) selected from Ni, Co, Mn, and Al; and w denotes a numeral in a range from −0.1 to 0.8; and the alloy have a composition as a whole defined by the general formula R1xR2yR3z, wherein 15.8≤x≤17.8, 3.4≤y≤5.0, 78.8≤z≤79.6, and x+y+z=100; R1 denotes one or more element(s) selected from rare earth elements including Y (yttrium); R2 denotes an Mg element, R3 denotes one or more element(s) selected from Ni, Co, Mn, and Al; z is 0.5 or higher when it denotes the stoichiometric number of Mn+Al; z is 4.1 or lower when it denotes the stoichiometric number of Al.
CN102660700A discloses an AB3 type hydrogen storage alloy and preparation method thereof. The chemical formula of the AB3 type hydrogen storage alloy is La0.35Pr0.30MgxNi2.90Al0.30, wherein x=0.30˜0.35.
CN102195041A discloses a hydrogen storage alloy for an alkaline storage battery, the composition of which conforms to the general formula LaxReyMg1-x-yNin-m-vAlmTv (Re: rare earth elements including Y; T: Co, Mn, Zn; 0.17≤x≤0.64, 3.5≤n≤3.8, 0.06≤m≤0.22, v≥0), and the alloy's main phase has a A5B19-type crystal structure.
CN103326004A discloses an A2B7 hydrogen storage alloy for a nickel metal hydride battery and preparation method thereof. The alloy conforms to the structural general formula: LnaMgbNixYyZz, wherein Ln denotes at least one element selected from rare earth elements; Y denotes least one element selected from Al, Co, Nb, V, Fe, Cu, Zn, As, Ga, Mo, Sn, In, W, Si and P; Z denotes at least one element selected from Ag, Sr and Ge; 0.5≤a<2, 0<b<1, 5<X+Y+Z<9, 0<Y<3, 0<Z<1.
The above alloys do not contain Y element, or do not contain Zr element, or do not contain Ti element. However, they all contain alkaline earth metals or magnesium element. Because the vapor pressure of active metal element magnesium is high, the difficulty of manufacturing the alloy is increased, and the composition of the alloy is difficult to control. The escaped micro-fine magnesium powder is flammable and combustible, which is a potential safety hazards.
Researches of “An electrochemical study of new La1-xCexY2Ni9 (0≤x≤1) hydrogen storage alloys” (Electrochimica Acta, 46 (2001): 2385-2393) and “New ternary intermetallic compounds belonging to the R—Y—Ni(R═La, Ce) system as negative material electrodes for Ni-MH batteries” (Journal of Alloys and Compounds, 330-332 (2002): 782-786) report an AB3 type La—Y—Ni hydrogen storage alloy. Nevertheless, the alloy doesn't contain Mn and Al, and its maximum hydrogen storage capacity is only 260 mAh·g−1.